It all depends on the context and tone. Where I come from, it's usually used by hardmen when threatening each other. I picture Ray Winstone saying something like, "I'd leave that gun where it is, Sunshine."

what did he say exactly. Context is indeed key but usually the word "sunshine" is more sarcastic than flirty. I cannot imagine any scenario that if someone called me sunshine, I would take it as flirting because in my society it isn't. There are so many better words to flirt with.

Need context. Where I come from, it can mean the same as the innocent "darlin', sweetheart, hon', or even gorgeous" that the waitress or hair stylist calls me. My father-in-law (alzheimer's now) used to address me as "Hey, beautiful", while I called him "hiya, handsome" innocently in front of my husband.

But I've also heard it used when think what someone is doing/about to do is not very bright, or when they're annoyed with you. "So what time do you call this, sunshine?" Which means you're being naive or lacking self-awareness when the situation dictates, otherwise.

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